Adhesive pulse oximeter sensor with reusable portion

ABSTRACT

A pulse oximeter sensor that is designed to surround an appendage of the patient, such as a finger, toe or foot is disclosed. The sensor has a reusable member which preferably includes a photodetector. A disposable, flexible member preferably contains the photoemitter and can be wrapped around the patient&#39;s appendage to secure it to the appendage and the reusable member. When secured, the photoemitter and photodetector end up on opposite sides of the appendage. The disposable member connects to the reusable member to establish electrical contact. The reusable member is connected to a cable which can be plugged into a sensor monitoring system.

BACKGROUND OF THE INVENTION

This is a continuation-in-part of patent application Ser. No.07/600,541, filed Oct. 19, 1990, now abandoned.

This invention relates to sensors for use with non-invasive pulsemonitors such as plethysmographs or pulse oximeters.

A plethysmograph is a pulse monitor The plethysmograph sensor shineslight into the patient's tissue, and the light transmitted through thetissue is received by a photodetector. The photodetector generateselectrical signals corresponding to the transmitted light levels andtransmits the signals to a monitor for processing. Arterial blood willabsorb some of the light, with more light being absorbed when there ismore blood. Thus, changes in the amount of transmitted light are relatedto pulses of arterial blood in the illuminated tissue.

A pulse oximeter is a device for noninvasively determining the oxygensaturation of arterial blood. The pulse oximeter sensor shines light attwo different wavelengths (one in the red range, the other in theinfrared range) through a portion of the patient's blood-perfusedtissue. The red and infrared light transmitted through the tissue isdetected by a photodetector. The amount of light absorbed varies withthe amount of oxygen in the blood, and varies differently for red andinfrared light. The pulse oximeter monitor computes blood oxygensaturation based on the changes in the two detected light levels betweentwo points in time.

There are several types of sensors for plethysmographs and pulseoximeters. One is a surface sensor in which the light emitter and thephotodetector are mounted on the same sensor face. The sensor isattached to the patient with both the light emitter and the detector onthe same side of the patient's appendage (e.g., on the patient'sforehead). This type of sensor detects light reflected back from thetissue, rather than light transmitted through an appendage. The signaldetected will thus be weaker in most cases. The sensor is typicallyattached with a strap, headband or tape over the sensor, or an adhesivepad between the sensor and the skin.

Another type of sensor is a clamp design, such as that described in U.S.Pat. No. 4,685,464. The durable sensor described in that patent hasdeformable pads creating conforming tissue contacting surfaces to whichthe emitters and photodetector are secured. The deformable pads aredisposed in a hinged rigid housing that clips on the patient like aclothes pin. This relies on a clamping force to secure the sensor to thepatient. The force of the sensor against the patient's tissue couldreduce the flow of blood to that region. This exsanguination of thetissue beneath the sensor adversely affects pulse detection and analysisby suppressing the pulse in that portion of the tissue. As a result, thesensor site must typically be checked or moved every four hours toinsure adequate perfusion. Because of its relatively large mass,however, the clamp design is more susceptible to signal-distortingmotion artifact, i.e., differential motion between the sensor and thepatient.

A third sensor design is described in U.S. Pat. No. 4,830,014. Theconformable sensor described in that patent has emitters and aphotodetector mounted in the same side of a flexible web. The web wrapsaround a portion of the patient's tissue (such as a finger) so that thelight from the emitters must travel through the tissue before reachingthe detector. The web attaches to the skin with an adhesive surface onthe emitter and detector side of the web. Because of its relatively lowmass and the adhesive, this sensor adheres closely to the patient's skinand minimizes the effects of motion artifact. In addition, itsflexibility and use of adhesive to secure it minimizes theexsanguination caused by rigid sensors. Thus the sensor site typicallyonly needs to be checked every eight hours. Conformable sensors,however, are typically restricted to one application due in part to adecrease in adhesive effectiveness with each application and in part todifficulties in cleaning and sterilization for reuse. Replacement of thesensor after only one use can make pulse oximetry expensive.

SUMMARY OF THE INVENTION

The present invention provides a pulse oximeter sensor that is designedto surround an appendage of the patient, such as a finger, toe or foot.The sensor has a reusable member which preferably includes aphotodetector. A disposable, flexible member preferably contains thephotoemitter and can be wrapped around the patient's appendage to secureit to the appendage and the reusable member. When secured, thephotoemitter and photodetector end up on opposite sides of theappendage. The disposable member connects to the reusable member toestablish electrical contact. The reusable member is connected to acable which can be plugged into a sensor monitoring system.

In the preferred embodiment, the flexible member is a flexible adhesiveweb with arms extending laterally from a central portion. The reusablemember is preferably a rigid housing with a deformable pad forcontacting the appendage.

To attach the sensor to the patient, the flexible web is adhesivelyattached to one side of the patient's appendage, and the rigid housingis placed on the other side directly opposite the flexible web. The armsextend around the appendage to adhesively hold the conformable pad ofthe rigid housing against the appendage. By reducing the mass of thesensor and by adhesively attaching the emitters to the skin, thisconfiguration minimizes motion artifact by reducing the relativemovement between the sensor and the patient's skin experienced byprevious clamp-type sensors. In addition, the flexible web andconformable surface of the rigid housing minimize exsanguination of thetissue beneath the sensor. Since the sensor relies on adhesion to secureit to the patient, the sensor site should not need to be checked asoften as for a clamping-type sensor.

After use, the flexible web may be separated from the rigid housing, therigid housing cleaned, and a new flexible web attached to the rigidhousing. The fresh adhesive on the new flexible web provides a morereliable bond between the sensor and the patient than the adhesive onthe previously-used web. In addition, since the flexible web covers fourout of the five surfaces of the patient's appendage (including, whenworn on the finger, the cuticle and subungual region), one time use ofthe flexible portion of the sensor minimizes cross-contamination betweenpatients when the sensor is reused. Furthermore, because a portion ofthe sensor may be cleaned and reused, this new sensor design reduces thecost of using flexible sensors.

The electrical connection between the flexible web and the rigid housingis preferably made with a tab extending from the flexible web havingconductive traces printed on it which connect to the photoemitter. Theconductive traces are inserted into a channel in the back of the housingwhich is covered by a bridge. Underneath the bridge are a series ofelectrical contacts for making connection with the conductive traces.The tab contains an internal resilient foam which is compressed as it isinserted between the housing and the bridge, and exerts an outward forceto maintain the tab in place and create an electrical connection betweenthe conductive traces and the contacts.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sensor according to the presentinvention;

FIG. 2 is a perspective view of the sensor of FIG. 1 showing theflexible web being wrapped around a finger; and

FIG. 3 is a perspective view of the separated disposable and reusablemembers of FIG. 1 illustrating how the connection is made.

DETAIL OF THE PREFERRED EMBODIMENT

FIG. 1 shows a sensor 10 according to the present invention. Sensor 10consists of a flexible, disposable webbing 12 and a reusable housing 14.Housing 14 includes a rigid portion 16 and a deformable pad 18. Apatient's finger 20, shown in phantom, is shown placed on top ofdeformable pad 18.

Flexible web 12 includes a photoemitter 22, which preferably includestwo photoemitters, one for red light and one for infrared light. Aphotodetector 24 is included in deformable pad 18. A copper grid 23 isdisposed over photodetector 24. A transparent window 25 coversphotodetector 24. All or substantially all of the portion of window 25extending beyond photodetector 24 is colored black. In addition, a blackarea 29 is printed on the underside of foam layer 28. Grid 23,photodetector 24 and photoemitter 22 are electrically connected to asensor monitoring system through conductors in a cable 26 connected tohousing 14.

Grid 23 is a Faraday shield (electrostatic screen) connected to groundfor reducing interference. The thin window 25 extends over the coppergrid so that the grid will not bulge out pad 18. Before the blackcoating was added, shift errors in the data values were noticed. Theblack coating eliminated these errors. The reason is not certain, butthe coating over the window may prevent reflections from most of thecopper, while the black coating on the foam layer 28 may prevent lightfrom being shunted through the foam layer to the detector, bypassing thefinger.

Webbing 12 has a top foam layer 28 with an adhesive surface. Before use,this adhesive layer is covered with protective plastic (not shown),which is peeled off for use.

FIG. 2 illustrates how the flexible webbing 12 is bent over and attachedto finger 20. A first arm 30 of the flexible web is wrapped around theside of housing 14 and will continue to be wrapped around its bottom inthe direction of arrow 32. Similarly, the other arm 34 will be wrappedaround finger 20 and housing 14. As can be seen, photoemitters 22, shownin phantom, are now on top of the finger, directly oppositephotodetector 24, which is not visible in this view. As can be seen,only the bottom of finger 20 contacts deformable pad 18. At least thetop of the finger will be adhered to by web 12. The sides and front mayalso be adhered to, depending on the shape of the finger and how thesensor is attached. The top is the portion which is most important to beadhering, since it contains the photoemitter which should not moverelative to the finger. This provides a secure connection which reducesmotion artifacts and puts the disposable, flexible portion in contactwith most of the surfaces of the finger so that it is exposed to morecontamination than the reusable portion.

FIG. 3 illustrates the electrical connection between flexible web 12 andrigid housing 14. FIG. 3 shows adhesive layer 28 partially peeled backfrom a web base 36. In between web base 36 and adhesive layer 28, anelongate plastic substrate 38 is placed, with a series of conductivetraces 40 on its top surface. Two conductive traces connect tophotoemitters 22, and two connect to a calibration resistor 55,described below. Elongate plastic substrate 38 forms a tail 42. Web base36 can be just large enough to hold tail 42 to adhesive layer 28, asshown, or could conform to the shape of adhesive layer 28. Web base 36has an adhesive surface for holding tail 42 to layer 28.

A compressible foam member 44 is placed between the halves of tail 42.In the preferred embodiment, the foam is made of Poron foam from Roger'sCorp. A pair of tabs 46 extend from the top half of the tail having theconductive traces. The tabs and the foam member provide part of theattachment mechanism as explained below.

A channel 48 is formed on the bottom side of the rigid housing 16,opposite deformable pad 18. A series of electrical contacts 50 (shown inphantom) are located in the channel. The contacts are covered by abridge 52 extending across the housing. A pair of grooves 54 are formedin the channel. The grooves are slightly larger than the tabs 46 on theflexible web.

To connect the flexible web to the rigid housing, the tail 42 of theflexible circuit is inserted into the space beneath bridge 52. As thetail moves forward, the plastic foam 44 compresses. As the tail's tabs46 move over the channel's grooves 54, the spring action of the foampushes the tabs into the grooves. The tabs and grooves ensure that theflexible circuit is not inserted too far and prevent inadvertent removalof the flexible circuit. The spring action of the foam also pushes oneset of contacts against the other to enhance the electrical connection.In addition, the scraping action of one set of contacts against theother during insertion and withdrawal of the flexible circuit will helpremove any oxidation or debris on the contacts. To remove, the tabs arelifted out of the grooves by pulling the flexible web away from thehousing and the tail is withdrawn from the space beneath the bridge.

Cable 26 contains 6 wires. Two are connected to calibration resistor 55through two of contacts 50 and conductive traces 40. Two are connectedto photoemitters 22 through the other two of contacts 50 and conductivetraces 40. The remaining two wires are connected to photodetector 24.

In the preferred embodiment, the plastic substrate is formed from white,substantially opaque polyester. White nylon may also be used, or a clearplastic. The adhesive may be white, with a clear window for thephotoemitters.

The preferred embodiment of the sensor according to this inventionincludes an encoding/decoding system such as that described in U.S. Pat.No. 4,621,643. The flexible web supports an encoding resistor 55 inelectrical communication with the monitor. As explained in that patent,the value of the resistor is selected to match the wavelengths of thered and infrared LED's. That patent also describes the necessary sensormonitoring electronics.

In an alternative embodiment, the sensor's photodetector may be mountedin the flexible web with the emitters and the encoding resistor mountedin the rigid housing.

In the preferred embodiment, the rigid housing is made from injectionmolded polycarbonate. Alternatively, injection molded ABS plastic may beused. U.S. Pat. No. 4,685,464 contains additional details onconstruction of a rigid housing and deformable pad including theplacement of the photodetector.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. For example, thecompression effect of foam 44 could be obtained instead by making bridge52 a spring-action clip, which is opened by holding one end down duringinsertion and then released, with a spring on the clip holding the tabin place. Other variations in the way electrical contact is made arealso possible. Instead of the adhesive layer, the flexible portion couldbe attached to the finger and rigid housing using velcro or othersecuring mechanisms. The flexible web could be made of foil or othercolor materials than white or clear. The sensor could be a surfacesensor, with adhesive for reducing motion artifact on the disposableportion. Accordingly, the disclosure of a preferred embodiment of theinvention is intended to be illustrative, but not limiting, of the scopeof the invention which is set forth in the following claims.

What is claimed is:
 1. A sensor for attaching to a patient forelectrooptical measurement of blood characteristics, comprising:areusable member including a first electronic means for emitting ordetecting electromagnetic radiation; conducting means, connected to saidreusable member, for electrically connecting said first electronic meansto an external sensor monitoring system; a disposable, flexible memberincluding a second electronic means for detecting electromagneticradiation emitted by said first electronic means or emittingelectromagnetic radiation to be detected by said first electronic means;means for removably coupling said flexible member to said reusablemember to provide a connection between said second electronic means andsaid conducting means; and means for securing said disposable, flexiblemember and said reusable member to said patient.
 2. The sensor of claim1 wherein said means for securing comprises an adhesive on saiddisposable, flexible member.
 3. The sensor of claim 1 wherein saidsecond electronic means is at least one photemitter.
 4. The sensor ofclaim 1 wherein said means for removably coupling comprises a tailextending from said disposable, flexible member having at least oneexposed first electrical conductor, at least one exposed secondelectrical conductor extending from said reusable member, and a bridgemeans connected to said reusable member and extending across said secondelectrical conductor for allowing said tail to be inserted between saidbridge means and said second conductor.
 5. The sensor of claim 4 whereinsaid tail includes resilient means for applying force between saidsecond conductor and said bridge means to hold said tail in place. 6.The sensor of claim 1 wherein said reusable member comprises a rigidhousing and a deformable means, attached to said housing, for securelygripping and complying to an appendage of said patient.
 7. The sensor ofclaim 1 wherein said second electronic means comprises a red lightphotoemitter and an infrared photoemitter.
 8. The sensor of claim 7wherein said first electronic means comprises a photodetector.
 9. Thesensor of claim 1 wherein said means for securing attaches said sensorto an appendage of said patient so that said first electronic means ison an opposite side of said appendage from said second electronic means.10. The senor of claim 1 further comprising a black coating on saidflexible member around said second electronic means.
 11. The sensor ofclaim 1 further comprising:an electrostatic screen adjacent said firstelectronic means; and a thin film covering said first electronic meansand at least a portion of said electrostatic screen, said film beingtransparent over said first electronic means and opaque over saidportion of said electrostatic screen.
 12. A sensor for attaching to anappendage of a patient for electrooptical measurement of bloodcharacteristics, comprising:a reusable member including a firstelectronic device for emitting or detecting light; conducting means forelectrically connecting said first electronic device to an externalsensor monitoring system; a disposable, flexible member including asecond electronic device for detecting light emitted by said firstelectronic device or emitting light to be detected by said firstelectronic device; a tail extending from said disposable, flexiblemember having at least one exposed first electrical conductor, at leastone exposed second electrical conductor extending from said reusablemember, and a bridge connected to said reusable member and extendingacross said second electrical conductor to allow said tail to beinserted between said bridge and said second conductor; means forsecuring said disposable, flexible member to said appendage and saidreusable member so that said first electronic device is on an oppositeside of said appendage from said second electronic device.
 13. Thesensor of claim 12 wherein said means for securing comprises an adhesiveon said disposable, flexible member.
 14. The sensor of claim 12 whereinsaid second electronic device is a photoemitter.
 15. The sensor of claim12 wherein said tail includes resilient means for applying force betweensaid second conductor and said bridge to hold said tail in place.
 16. Asensor for attaching to an appendage of a patient for electroopticalmeasurement of blood characteristics, comprising:a reusable memberincluding a photodetector; conducting means, connected to said reusablemember, for electrically connecting said photodetector to an externalsensor monitoring system; a disposable, flexible member including atleast one photoemitter for emitting light to be detected by saidphotodetector; means for removably coupling said flexible member to saidreusable member to provide a connection between said photoemitter andsaid conducting means; and an adhesive coating on said disposable,flexible member for securing said disposable, flexible member to saidappendage and said reusable member so that said photodetector is on anopposite side of said appendage from said photoemitter.
 17. A sensor forattaching to an appendage of a patient for electrooptical measurement ofblood characteristics, comprising:a reusable member including at leastone photodetector, said reusable member including a rigid housing and adeformable means, attached to said housing, for securely gripping andcomplying to said patient's appendage; conducting means, connected tosaid reusable member, for electrically connecting said photodetector toan external sensor monitoring system; a disposable, flexible memberincluding a red light photoemitter and an infrared photoemitter foremitting light to be detected by said photodetector; a tail extendingfrom said disposable, flexible member having at least one exposed firstelectrical conductor; at least one exposed second electrical conductorextending from said rigid housing; a bridge connected to said rigidhousing and extending across said second electrical conductor to allowsaid tail to be inserted between said bridge and said second conductor;resilient means, coupled to said tail, for applying force between saidsecond conductor and said bridge to hold said tail in place; and anadhesive coating on said disposable, flexible member for securing saiddisposable, flexible member to said appendage and said reusable memberso that said photoemitters are on an opposite side of said appendagefrom said photodetector.